This work presents the results of investigation of the weathering products originated from two tailing ponds situated in Spišsko-Gemerské rudohorie, near the villages of Rudňany and Slovinky. The tailings are near-neutral or slightly alkaline (pH = 7.2-8.8) because the acidity generated by the decomposition of the sulfides is efficiently neutralized by the abundant carbonates. The most frequent primary gangue minerals are siderite, quartz, barite, and muscovite. The prevailing primary sulfides in both tailings are pyrite and chalcopyrite, less common are tetrahedrite and arsenopyrite. The most frequent secondary minerals (i.e., minerals formed in the tailings, not in the oxidation zone of the deposits) at both localities are iron oxides, either goethite or amorphous and poorly crystalline hydrous ferric oxide. Other minerals (cuprite, malachite and delafossite) are minor or rare and occur only in Slovinky, and probably come from the oxidation zone of deposit. All these minerals were identified by X-ray microdiffraction. The iron oxides are enriched in a suite of elements, including Ca, Mg, Si, Mn, minor As, Cu, Sb in Rudňany and in Cu, Si, Mg, Mn minor Sb, Ca, As a Zn in Slovinky. The transformations of the poorly crystalline hydrous ferric oxide to goethite and maturation of goethite is controlled by both high-valence tetrahedral cations (Si, As, P) and lower-valence octahedral cations (Cu), as shown by the measurements of the size of coherently diffracting domains in goethite and the chemical composition of goethite. The iron oxides, by the virtue of their adsorption capacity, prevent separate minerals of many metals and metalloids (Cu, Ca, As, Sb) to nucleate and grow, and therefore control the entire system of processes running in the environment of tailing impoundments. Key words: tailing impundments, weathering products, goethite, Cu-Fe deposits